The present invention relates to an echo cancellation device, an echo cancellation program, and an echo cancellation method, and more particularly, to an echo cancellation device, an echo cancellation program, and an echo cancellation method which reduce echo signal components generated when a voice signal output from the echo cancellation device is input through a microphone of the echo cancellation device.
In recent years, hands-free communication devices have been used in many cases as auxiliary devices for making a call without the need to hold a communication device, such as a cellular phone, in a user's hand. The hands-free communication devices are grouped into a head set type in which a headset that is a combination of an earphone and a microphone is connected to a cellular phone or the like, and a speaker type in which a loudspeaker and a microphone are connected to a cellular phone or the like. Among the hands-free communication devices, the hands-free communication device of the type using a loudspeaker and a microphone prevents a cable or the like from getting entangled with a user. Accordingly, this type of hands-free communication device is particularly suitable for use in driving an automobile or the like.
However, in the speaker-type hands-free devices, a voice signal transmitted from the loudspeaker comes into the microphone, so that an echo to be transmitted to a call destination is generated. If an echo is generated during a call, the voice signals resonate with each other and the clarity of a speech may deteriorate, or howling may occur, which makes it difficult to continue the call. Techniques for improving the clarity of a speech by solving the problem of echo and the like are disclosed in, for example, Japanese Unexamined Patent Application Publication No. H07-221832 and Japanese Unexamined Patent Application Publication No. 2011-130170.
Japanese Unexamined Patent Application Publication No. H07-221832 discloses a frequency characteristic control method for obtaining a sufficient clarity of a speech even when the level of ambient noise is high. In Japanese Unexamined Patent Application Publication No. H07-221832, frequency spectrums of a transmitting acoustic signal and an incoming acoustic signal are detected. In accordance with the magnitude of a level difference between the frequency spectrums, the incoming call frequency spectrum is set to be equal to or higher than the level of a noise frequency spectrum in a frequency range equal to or higher than a lower-limit frequency necessary for obtaining a clarity of a speech of 70% or more. When a maximum level difference between the noise frequency spectrum and the incoming call frequency spectrum is equal to or lower than a predetermined limit value, the component level of the incoming call frequency spectrum lower than the required lower-limit frequency is increased according to the amount of component level change. When the maximum level difference exceeds the predetermined limit value, the component level of the incoming call frequency spectrum lower than the required lower-limit frequency is reduced, and at the same time, the component level of the incoming call frequency spectrum equal to or higher than the required lower-limit frequency is increased.
Japanese Unexamined Patent Application Publication No. 2011-130170 discloses an echo canceller that removes an echo. The echo canceller disclosed in Japanese Unexamined Patent Application Publication No. 2011-130170 includes: specific frequency component removing means for outputting, to an echo path, a signal in which a specific frequency component of a specific frequency is removed from a received signal; specific frequency component detection means for detecting, from a transmitting signal, a frequency component having the same frequency as the specific frequency removed by the specific frequency component removing means; noise calculation means for obtaining noise power based on the power of the specific frequency component detected by the specific frequency component detection means, and obtaining a total power including noise and an echo component on the basis of the power of frequency components including the echo component; and control parameter calculation means for obtaining a control parameter for the echo canceller by using the noise power and the total power obtained by the noise calculation means.